1. Field of the Invention
The present invention relates to a webbing retractor which, when a vehicle rapidly decelerates, tenses a webbing in a direction of restraining a vehicle occupant. In particular, the present invention relates to a webbing retractor which, when pulling-out of a webbing is impeded, allows the webbing to be pulled-out by a predetermined amount and can absorb energy.
2. Description of the Related Art
A webbing retractor which forms a seat belt device of a vehicle is usually provided with a lock mechanism which, at the time the vehicle rapidly decelerates, locks a spool (take-up shaft) so as to impede pulling-out of a webbing.
One example of such a lock mechanism is a type which includes a lock base and a lock device. The lock base is disposed coaxially with the spool and is connected so as to be integral with the spool. At the time of rapid deceleration of the vehicle, the lock device engages with the lock base so as to impede rotation of the lock base, and indirectly impedes rotation of the spool.
Further, such webbing retractors are equipped with a so-called force limiter mechanism which, when pulling-out of the webbing is impeded, allow the webbing to be pulled-out by a predetermined amount in order to limit the load applied to the vehicle occupant by the webbing to a given amount or less, and absorb energy. An example of this force limiter mechanism is a structure in which one end portion of the torsion bar, which is disposed coaxially with the spool, is fixed to the spool, and the other end portion is connected so as to be integral with the aforementioned lock base. In this type of force limiter mechanism, relative rotation of the spool with respect to the lock base arises due to the locking of the lock base by the lock device at the time when the vehicle rapidly decelerates, and due to the tensile force applied to the webbing belt from the body of the vehicle occupant which attempts to move toward the front of the vehicle when the vehicle rapidly decelerates. Due to the torsion bar being deformed in a twisting direction by the rotational force of this relative rotation, a predetermined amount of rotation of the spool is permitted while energy is absorbed.
This absorbed energy is determined by the product of the load applied to the webbing (force limiter load) and the webbing pull-out amount (amount of rotation of the spool). At the webbing retractor, the force limiter load and the allowable amount of rotation of the spool (the twisting limit of the torsion bar) are given, and there are limits on the amount of energy which can be absorbed.
Higher energy absorption amounts are preferable. Thus, structures have been conceived of in which an energy absorbing member other than the torsion bar, which energy absorbing member absorbs energy by deforming, is provided between the lock base and the spool. However, with such an energy absorbing member, there is a high possibility that, due to the spool rotating relative to the lock base, stress such as shearing stress or the like will concentrate at a portion of the energy absorbing member such that the energy absorbing member will break. If the energy absorbing member breaks, after breakage, energy absorption by the energy absorbing member is not possible. Thus, further improvement is desired.
In view of the aforementioned, an object of the present invention is to provide a webbing retractor having a force limiter mechanism whose energy absorption amount is large and which can reliably absorb energy.
A webbing retractor relating to a first aspect of the present invention is a retractor of a webbing belt which is elongated and belt-shaped and restrains a body of a vehicle occupant in a state in which the webbing belt is applied to the vehicle occupant, the webbing retractor comprising: (a) a take-up shaft to which a proximal end portion of the webbing belt is anchored, and due to the take-up shaft rotating in one direction around an axis of the take-up shaft, the take-up shaft takes-up the webbing belt from a proximal end side, and due to tensile force, toward a distal end side which is a side opposite to the proximal end portion, being applied to the webbing belt, rotational force in a pull-out direction, which is a direction opposite to a take-up direction, is applied to the take-up shaft; (b) a rotating body which is provided at a side of an axial direction of the take-up shaft so as to be coaxial with and freely rotatable with respect to the take-up shaft; (c) a lock device which restricts rotation of the rotating body at a time a vehicle rapidly decelerates; (d) an energy absorbing member having a fixing portion which is provided eccentric to the take-up shaft and which is fixed to one of the take-up shaft and the rotating body, and the energy absorbing member has a curved portion which is bent from the fixed portion and which curves around an axial center of the take-up shaft in a direction of rotation of another of the take-up shaft and the rotating body with respect to the one of the take-up shaft and the rotating body at a time when the take-up shaft rotates in the pull-out direction relative to the rotating body, and the energy absorbing member has a fit-in portion which is bent from an end portion of the curved portion at a side opposite the fixing portion and which is inserted into the other of the take-up shaft and the rotating body; and (e) a forcibly pulling-out device which, as the take-up shaft rotates in the pull-out direction relative to the rotating body, rotates and pulls the fit-in portion out of the other of the take-up shaft and the rotating body, and forcibly curves the fit-in portion along an extension of a direction of curving of the curved portion.
In the webbing retractor having the above-described structure, when the take-up shaft rotates in-the pull-out direction in a state in which the lock device engages with the rotating body and rotation of the rotating body is limited in a case in which the vehicle rapidly decelerates, the take-up shaft rotates relative to the rotating body. At this time, the fit-in portion of the energy absorbing member, which is fit into the other of take-up shaft and the rotating body, attempts to rotate relative to the fixing portion of the energy absorbing member fixed to the one of the take-up shaft and the rotating body.
However, the curved portion is formed so as to be bent from the fixing portion, and the fit-in portion is formed so as to be bent from the curved portion. (Namely, the fixing portion and the fit-in portion are integral via the curved portion.) Thus, the fit-in portion cannot merely rotate relative to the fixing portion, and the fit-in portion is forcibly pulled-out by the forcibly pulling-out device. Moreover, the fit-in portion, which is bent from the curved portion, is forcibly deformed and curved along an imaginary line extending in the curving direction of the curved portion. The take-up shaft can rotate in the pull-out direction by an amount corresponding to the amount that the fit-in portion is pulled-out by the forcibly pulling-out device. Pulling-out of the webbing belt by an amount corresponding to the permitted amount of rotation is possible, and energy corresponding to an amount of deformation of the fit-in portion is absorbed.
In this way, for example, in a case in which another energy absorbing member is used such as a so-called torsion bar, which is provided at the substantial axial center of the take-up shaft in a state in which one end is fixed to the take-up shaft and the other end is fixed to the rotating body and which twistingly deforms due to relative rotation between the take-up shaft and the rotating body, the amount of absorbed energy, which is due to the energy absorbing effect due to the curving (deformation) of the fit-in portion, is added to the amount of absorbed energy, which is due to the energy absorbing effect of the energy absorbing member such as the torsion bar or the like. Thus, the overall amount of absorbed energy of the webbing retractor can be increased.
However, when the above-described energy absorbing member breaks due to stress concentrating at a portion thereof while the energy absorbing member is in the midst of deforming, no further energy can be absorbed. Thus, here, at the energy absorbing member of the present webbing retractor, the curved portion is provided between the fixing portion and the fit-in portion. As seen from the fixing portion, this curved portion is curved toward the aforementioned other of the take-up shaft and the rotating body (i.e., the one of the take-up shaft and the rotating body into which the fit-in portion is fit) when the take-up shaft rotates in the pull-out direction relative to the rotating body. Namely, when the curved portion is considered to be a portion of the fit-in portion, the curved portion can be considered to be a portion which is plastically deformed in advance in a direction of rotation of the aforementioned other of the take-up shaft and the rotating body (i.e., the one of the take-up shaft and the rotating body into which the fit-in portion is fit) when the take-up shaft rotates in the pull-out direction relative to the rotating body. By plastically deforming the curved portion in advance in this way, the curved portion can easily be deformed in the direction along this deformation, i.e., in the rotating direction of the other of the take-up shaft and the rotating body. Stress does not concentrate at one portion of the energy absorbing member, and the energy absorbing member does not break. In this way, energy can be reliably absorbed during a predetermined period of time which is set in advance.